The technical field of this invention is image processing and, more specifically, differential motion detection processes and devices. In particular, the invention relates to video telephones for transmitting both sound and images in real time over standard residential telephone lines.
When video conferencing was first demonstrated at the New York World's Fair in 1964, public expectations were raised that a new technology would soon render the telephone obsolete. However, various technical constraints have made video telephone systems prohibitively costly to all but a relatively small group. In particular, the amount of image data that must be transmitted has posed a most significant problem because such data far exceeds the capacity of existing standard residential telephone networks.
Researchers have attempted to overcome this obstacle in two ways: first, by using a different medium for data transmission to enable a higher data transfer rate; or second, by using image data manipulation techniques to compress the amount of data required to represent the image. This invention primarily is concerned with the latter approach of data compression.
Much of the work on video conferencing has been directed toward data transmission over special, high-quality transmission lines, such as fiber optics, which are capable of transmitting at least several times as much data as standard residential telephone lines. For example, an Integrated Switched Digital Network (ISDN) service is being implemented with a 64 kbit/sec. video transmission rate to replace, in some instances, the standard 3 kHz telephone lines that can handle at best up to about 20 kbit/sec., depending upon the signal processing employed. These special lines are relatively costly and currently are available only in limited areas.
An object of this invention is to provide an image data compression process to enable video telephones to be used over the present, copper-based, residential telephone network, as well as other low bandwidth transmission media.
Another object of this invention is to provide an inexpensive video telephone that may be used with standard video cameras and video display screens or personal computers to provide videoconferencing capabilities between users connected to the standard residential telephone network.